Proacrosin is activated to acrosin by acrolysin during sperm maturation (capacitation). The process appears to be ion initiated and regulated by inorganic and organic inhibitors. Synthetic inhibitors will be prepared to evaluate antifertility potential in vitro. Effective inhibitors will be tested in vivo in male rabbits. These inhibitors should provide the potential to permit evaluation of the time of proteolytic enzyme activation in mammalian fertilization.